1. Field of the Invention
The present invention relates to a hydraulic damping device, and more particularly to a hydraulic damping device including a partition having a central opening which is closed by an elastic rubber wall for both restraining low-frequency vibrations of large amplitude and absorbing high-frequency vibrations of small amplitude.
2. Description of the Prior Art
Conventional hydraulic damping devices are composed of a vessel-shaped thick rubber block which supports a vibrating body, and a deformable rubber sheet which closes an opening in the vessel-shaped thick rubber block. A main liquid chamber and an auxiliary liquid chamber are formed within the thick rubber black. The main liquid chamber is separated from the auxiliary liquid chamber by a partition which has a throttle passageway. The auxiliary liquid chamber is defined on its bottom side by the deformable rubber sheet. The hydraulic damping device damps vibration by forcing damping liquid enclosed within the main liquid chamber to flow into the auxiliary liquid chamber through the throttle passageway of the partition. Heretofore, various devices have been proposed to reduce high-frequency variations (Japanese unexamined patent publication Sho 60-121339, Japanese unexamined patent publication Sho 61-65934). These conventional devices are generally provided with an elastic rubber wall which closes an opening formed in the central portion of the partition.
When high-frequency vibrations of small amplitudes are input, the elastic rubber wall deforms and absorbs the build-up of the inner pressure of the main liquid chamber.
When low-frequency vibrations of large amplitudes are input to the hydraulic damping device, a higher pressure is built up in the main liquid chamber, as compared to high-frequency vibrations of small amplitude. This higher pressure is applied to the elastic rubber wall.
In order to resist that higher pressure in the above-described conventional devices, upper and lower surfaces of the elastic rubber wall have been formed into symmetric concave surfaces (see, for example, Japanese unexamined patent publication Sho 60-121339) or into parallel surfaces (see, for example, Japanese unexamined patent publication Sho 61-65934). Such elastic rubber walls which have concave or parallel surfaces, however, are likely to be fatigued as a result of the large shear stress generated in its peripheral portion, which is joined to the partition.